194 ANIMAL MOTION. 



however, mK. A. iv. c. 1, s. 6, that the octopus emits its 

 ink and also sea- water through its funnel. 



He was aware that most of his Ostrahoderma move but 

 slowly or are stationary, and that the pecten (Kteis) " flies" 

 some distance along the surface of the water by its own 

 efforts, and says that it is more capable of locomotion 

 than any other.* He also says that the sea-urchin travels 

 by using its spines as feet.t 



It has been stated already that Aristotle did not under- 

 stand the nature of nerves, some of which he probably saw. 

 It is interesting, therefore, to inquire by what means he 

 considered the various locomotory and other movements of 

 the body to be effected. Nowhere does he make this clear. 

 He says that the heart is the centre of motion, that it is 

 accordingly full of tendons, and that the motions of which 

 it is the centre are effected by contraction and relaxation.! 

 How the motions are transmitted from the heart to the 

 moving parts he does not explain, but he often mentions the 

 sinewy nature of the aorta, and especially its small branches, 

 and, in H. A. iii. c. 6, he says that the fibres are intermediate 

 between sinew and blood-vessel. He says, however, that 

 there is a want of continuity in the arrangement of the 

 sinews, § and this may be the reason why he abstained from 

 attempting to explain the mechanism of animal motion, 

 although he wrote a great deal about the motions themselves. 

 An important passage on this subject is in the De Anim. 

 Motione, c. 7, 701, one of the Aristotelian treatises which 

 was probably not vv^ritten by Aristotle himself. In that 

 passage it is stated that animals are moved by means of 

 bones and sinews, the bones being like the wooden and iron 

 frames of automata, and the sinews like cords by which the 

 frames are set in motion. It is also stated that the parts of 

 automata do not change in form and size, like the parts of 

 an animal, in which this change is caused by heat and 

 cold, which respectively effect expansion and relaxation 

 under the influence of imagination, sensibility, and thought. 



=•'■ H. A. ix. c. 25, s. 7. f Ibid. iv. c. 5. s. G. 



\ P, A. ii. c. 1, 647a; iii. c. 4, CG66. § H. A. iii. c, 5, s. 1. 



